Are Wildfires an Important Source of Metal Contamination of Boreal Lakes?Tuesday, November 20, 2018 - 15:00 to 15:19 Theatre 2
Boreal forests accumulate metal contaminants in soils and biomass over time because of the strong association of these metals to organic matter. Wildfires contribute to the remobilization of previously deposited local and long-range pollution. Strong evidence suggests that the concentration of some metals (e.g. Pb and Hg) has increased ubiquitously in the boreal forest over the Anthropocene in response to global pollution. The role of wildfires in metal transport associated with catchment erosion is well documented. However, studies have also demonstrated that wildfire ashes, transported atmospherically, can be a pathway for the transport of metal(oids) such as arsenic, cadmium, lead and mercury. If forest metal concentrations have increased in the Anthropocene, is it possible that wildfires have become an increasingly important process for the deposition of metals across the landscape, including lakes?
We investigated metal accumulation in sub-Arctic boreal lakes located at close distances (0.5 to 10 km) from fire scars of various age in the Yellowknife area (NT, Canada). Charcoal particle accumulation rates were examined in relation with observational fire records since 1965 to determine the occurrence of fire events in the sedimentary records. Preliminary results demonstrated good agreement between observational fire records and fire history determined from charcoal accumulation in the lake sediments. Our preliminary analysis revealed that wildfire events were not associated with important increases in metal concentration. Correlations between charcoal accumulation rates and metal concentrations in the sediments will be tested. Subsequent analysis will examine (1) if subtle changes on lake metal cycling, such as short-term increases in metal accumulation rate, could be influenced by wildfires and (2) if there is a temporal trend in the relationship between wildfire and lake metal loading over the last century.